Some tests contain halts other than at the beginning and end and these halts often have a specified duration i.e. 4 seconds. It is very common for riders to not properly time their halt and continue to the next movement too early.
The simplest way to try and ensure you halt for the correct time is to halt then say in your head “one elephant, two elephant, three elephant, four elephant” then continue on. This will be almost bang on 4 seconds and I can guarantee you the vast majority of judges will be saying something very similar in their heads as you perform your halt. Obviously you just need adjust to however long you are meant to perform the halt as required when counting!